The Evolution of Physics: From Aristotle to Galileo
ITEM 1: The Physical Throughout History
Aristotle’s Geocentric Model
Aristotle, one of the most influential figures in the history of physics, proposed a geocentric model of the universe. He believed that the Earth was stationary and located at the center of the universe, with the other planets, including the Sun, revolving around it in perfect circular orbits. This view was consistent with the Greek belief that the circle represented perfect motion and that the universe was finite.
Aristotle divided the universe into two distinct realms: the sublunary realm, encompassing everything within the Moon’s orbit, and the translunar realm, extending beyond the Moon’s orbit. He posited that the sublunary realm was characterized by change and decay, while the translunar realm was unchanging and perfect.
To explain the motion of celestial bodies, Aristotle proposed the existence of a substance called ether, which filled the translunar realm and facilitated the seamless circular motion of the planets. In contrast, the sublunary realm was governed by the four elements of earth, air, water, and fire, each seeking its natural place.
The Aristotelian-Ptolemaic System
Greek astronomers recognized a flaw in Aristotle’s theory: the observed motions of the planets were not perfectly circular. Ptolemy, an astronomer, refined the geocentric model by suggesting that the Earth was slightly offset from the center of the universe, allowing for non-circular planetary motions. This revised model became known as the Aristotelian-Ptolemaic system.
The Copernican Revolution
In the 15th century, Nicolaus Copernicus, a Polish priest, challenged the geocentric view by proposing a heliocentric model, placing the Sun at the center of the universe and the Earth as one of the planets revolving around it. Copernicus’s theory contradicted both Aristotle and the Church, leading him to delay the publication of his findings.
Galileo’s Defense of Heliocentrism
Galileo Galilei, inspired by Copernicus’s work, became a strong advocate for the heliocentric model. He conducted astronomical observations that supported the heliocentric theory and wrote a play defending it, which sparked a major dispute with the Church. The Church, upholding a literal interpretation of the Bible, argued that the Earth was stationary, as implied by the biblical passage where Joshua commanded the Sun to stand still.
Galileo’s defense of heliocentrism also faced opposition from humanists who believed that humans were the center of the universe and from physicists who lacked empirical evidence for the Earth’s motion. Despite facing persecution, Galileo’s contributions to physics and astronomy, including his work on motion and the pendulum, remain significant.
The New Science
Galileo’s work, along with the earlier ideas of William of Ockham, who proposed the principle of economy (nature operates in the simplest way possible), paved the way for a new scientific worldview. This new science was characterized by:
- The mathematization of reality, expressing knowledge in mathematical form.
- A focus on motion as the primary object of study.
- The absence of an absolute reference system, with laws remaining invariant across different systems.
- The explanation of phenomena through efficient causes and governing laws.
- A mechanistic view of the world, where humans are part of a larger machine, leading to a deterministic perspective.
The heliocentric model, initially proposed by Aristarchus of Samos but largely ignored, eventually gained acceptance, revolutionizing our understanding of the universe.